The title says it all... I've got an OS 21TM in a revo and it's loading up when running half throttle. Idle seems perfect, top end seems perfect... and the temps stay around 240 to 250. I'm using sigs car fuel that is 10% nitro, 20% oil, and 50/50 castor-Klotz mix. The glow plug is a traxxas medium/long. Midrange needle is in the stock position.

Before you tell me to switch fuels, let me just say that I've been using this fuel for the last 15 or 16 gallons with great results. The high oil content does have some drawbacks, but I have yet to scorch a piston and sleeve, and by removing the head shim I get more than enough power to compensate for the lack of nitro. I'm running the same fuel in a TRX 3.3 that has an OS 11k carb on it, and I don't have this sloppy midrange thing going on with it at all.

I did have sloppy midrange on the trx with the os carb at one point, but by moving the midrange needle to line the hole that goes through it with the HSN, the problem was cured and it tunes perfectly now. I'm thinking perhaps the fuel is thicker than most and not having that hole lined up caused some flow problems. This remedy doesn't seem to work on the OS 21TM though. Not sure why... unless I have a gob of old castor oil plugging the carb somewhere... never thought of that till just now. It's been about 2 years since I messed with any of this stuff... perhaps it's gooped up from sitting and causing my tuning problems...

I can only reinforce what you are already thinking....after a very short time the nitro of a fuel evaporates...then the methanol...if you let things sit for long enough then it is usually best to flush it trough first.
When you run a fuel with higher oil content then of course the needle settings will need to be richer due to the viscosity...
Still not too sure why you would be running a 20% oil content in a car though...

I can only reinforce what you are already thinking....after a very short time the nitro of a fuel evaporates...then the methanol...if you let things sit for long enough then it is usually best to flush it trough first.
When you run a fuel with higher oil content then of course the needle settings will need to be richer due to the viscosity...
Still not too sure why you would be running a 20% oil content in a car though...

Ya I know it's a lot of oil, and like I said it does have it's drawbacks... more difficulty in tuning being one of those... but this particular blend also has it's benefits such as all that good gooey castor oil. Mostly though, I like it because it seems high quality, and it's really inexpensive. Even with shipping costs, it's way less $$ than what I can get at the LHS. On top of that, this OS 21TM ponies up about as much as the drivetrain on the Revo can handle for any length of time. Even with this thick smokey fuel (which I love the smell of as it comes out the tailpipe) and just 10% nitro, the 21 doles out some serious abuse. I'm sure if I went to the track I would get hammered, but just bashing around with some buddies and their 20% traxxas fuel and their TRX 3.3's, there's no comparison... hands down the 21 is way more powerful.

Anyways...

I was able to pull the carb off this afternoon and tear it apart, and I found the problem... It wasn't gunked up at all... nice and clean. The issue was the hole in the fuel line nipple wasn't lined up with the hole in the HSN housing. I had checked the midrange needle to make sure it was lined up, but never thought to check the nipple. Normally, this would not be an issue with thinner fuel, but it definitely makes a difference with the Sigs... especially as the weather is getting cooler here. I lined everything up, retuned, and it ran great.